Knife sharpener



FIG. 1 is a top front perspective view of a knife sharpener, showing my new design;

FIG. 2 is a bottom, rear perspective view thereof;

FIG. 3 is a front elevation view thereof;

FIG. 4 is a rear elevation view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is a top plan view thereof;

FIG. 7 is a left end elevation view thereof;

FIG. 8 is a right end elevation view thereof, and,

FIG. 9 is a top, front perspective view thereof, in the folded condition.

The broken lines shown in the drawings illustrate portions of the knife sharpener that form no part of the claimed design. 

CLAIM The ornamental design for a knife sharpener, as shown and described. 